Process for removing iron carbonyl compounds from oxo reaction products



n wd St e Patent Karl Rehn, Hofheim (Taunus), and Gerhard Theilig, Frankfurt am Main, Germany, assignors to Farbwerke Hoechst Aktienge'sellschat't vormals Meister Lucius &'

Briining, Frankfurt am Main, Germany, a corporation of Germany No Drawing. Filed Dec. 16, 1957, Ser. No. 702,788 Claims priority, application Germany Dec. 19, 1956 7 Claims. (Cl. 260604) The present invention relates to a process for removing iron carbonyl compounds from products obtained by an addition reaction of carbon monoxide and hydrogen with olefins.

It is known that during the reaction of olefins with carbon monoxide and hydrogen at a raised temperature and elevated pressure oxygen-containing products, predominantly aldehydes, are formed in the presence of cobalt' carbonyl compounds of catalytic action. The portions of cobalt carbonyl compounds dissolved in the reaction product impair the storability of the crude aldehydes and aifect their isolation and interfere with their subsequent hydrogenation to alcohols. In general, the cobalt compounds are therefore removed from the crude aldehydes. It has, for example, been proposed to heat the crude aldehydes under reduced partial carbon monoxide pressure until thermal decomposition of the carbonyl compounds takes place with separation of cobalt metal or to treat the crude aldehydes with water or aqueous acids, if desired at raised temperature and elevated pressure, whereby filterable compounds or dissolved salts of cobalt are obtained. According to another process the crude aldehydes are contacted with gases containing oxygen in Order to convert the volatile carbonyl compounds dissolved therein into metal compounds which can be easily isolated.

Besides containing cobalt carbonyl compounds obtained from any desired cobalt compounds added, the crude aldehydes in practice always contain small amounts of dissolved carbonyl compounds of other metals. Said compounds are formed by the reciprocal action of the carbon monoxide with the material of the storage containers, pumps, pipes etc. Especially iron carbonyl often forms in the crude aldehydes in a concentration of 0.001 to 0.1% Fe (cf. U.S. Patent 2,721,136) and is to be removed therefrom. A simple thermal decomposition as it has often been suggested for the removal of cobalt carbonyl compounds does not lead to the desired obtainment of the entire yield of oxygen-containing products as it fails to destroy the considerably more stable iron carbonyl in a satisfactory manner (cf. U.S. Patent 2,604,491) and complete decomposition occurs only during the subsequent hydrogenation in which case the deposits of metallic iron either clog the preheater or damage the catalyst. The carbon monoxide set free by the decomposition contaminates the hydrogenation catalyst, especially if the hydrogen is recycled, and shortens its life.

Attempts have therefore been made to render the decomposition of the metal carbonyl compounds more complete by the supply of steam. Even in this case the course of the decomposition of the iron carbonyl is far from being as smooth as in the case of cobalt carbonyl compounds. Furthermore, the metals are obtained in the form of deposits so that filtrations and the use of carriers are necessary. The destruction of the iron carbonyl by means of mineral acids which has also been proposed 2 requires energetic conditions which easilygive rise to side reactions (cf. British Patent 667,824); besides, considerable losses especially in the aldehydes with 3 to .5 carbon atoms occur owing .to the solubility of these'aldehydes in the acids and wash waters. A further proposal to remove theiron carbonyl by a treatment with alkalisis hardly applicable to these aldehydes of great reactivity due to their tendency to form aldols. According to another process the metal carbonyl compounds contained in the crude aldehyde are oxidized with air, preferably in the presence of organic acids. This process, however, does not result in the desired removal of the-iron carbonyl unless one puts up with losses in yield. The subsequent distillation yields a yellow aldehyde from which ferric hydroxide separates on storing which gives riseto obstructions and can only be removed by a further'distillation or filtration. Even a distillation of the oxidized crude aldehyde in'the presence of steam leads to aniron-containing aldehyde, also if a mineral acid is added to the material to be distilled.

It has furthermore been described to regenerate the spent aqueous solution obtained in the addition reaction of carbon monoxide and hydrogen with olefins after separation of the organic reaction products and containing the iron dissolved in the form of sulfate, by adding cobalt carbonate in an amount equivalent to the iron content and by intense stirring, while blowing in air, in order to precipitate the dissolved iron compounds. Nothing has,

howeverflbeen said about the purification of the organic reaction product'by means of a salt of trivalent cobalt.

These cobaltic salts canbe obtained in a dissolved form in various ways, for example by oxidation of cobaltous salt solutions with hydrogen peroxide.

The cobaltic salts to be used for the process of the invention can be obtained in a particularly simple manner by blowing oxygen or gases containing oxygen, for example air, into the crude reaction products obtained by an addition reaction of water gas with olefins, while proceeding in the presence of water and maintaining a concentration of hydrogen ions suitable for the rapid conversion of cobalt carbonyl compounds into salts of trivalent cobalt. The water is suitably present in such an amount that the resultant metal compounds leave the oxidation zone in a dissolved form. The quantity of water may amount to 0.1 to 5%, depending on the metal content of the crude aldehyde. The water may either be added immediately before the oxidation or may be contained in a homogeneous or dispersed phase in the crude product obtained by the addition reaction of water gas with olefins if it has been added prior to the addition reaction or formed in the addition stage due to side reactions. In this case it may be superfluous to add a further amount of water.

It is, however, also possible to add a considerably greater amount of water and to proceed in a dispersed mixture if this is desired in order to control the oxidation temperature or with a view to the further treatment of the metal salt solutions. The pH value of the oxidation zone should be selected in such a manner that the salts of the iron and of the cobalt which have formed remain in solution. With too low a pH value,- however, the salts of the trivalent cobalt are formed too slowly in which case a marked oxidation of the crude aldehyde occurs already before the complete destruction of the iron car- -bonyl. It is therefore of advantage to proceed at a pH Patented Dec. 6, 1960.

tial oxidation of the aldehyde does not yet take place, i.e. in general, at a pH value of above 3. It is furthermore of advantage to use a pH value at which substantial formation of aldols does not yet take place, i.e. in general at a pH value below 9. A still more rapid formation of cobaltic salts is obtained at pH values ranging from 4 to 6. The optimum concentration of hydrogen ions can be obtained by the addition of water, aqueous solutions, lyes or salts, for example by buffering the aqueous phase. In the case of some crude aldehydes it is sufiicient to add pure water if the constituents of the crude product enable an appropriate adjustment of the pH value to be obtained. It can be ascertained for any desired crude aldehyde by a short preliminary test whether or not a buffering is necessary for the rapid formation of cobaltic salts and which kind of buffering is to be applied.

The influence of the pH value upon the formation of the cobaltic salts necessary for the destruction of the iron carbonyl can be seen from the following series of experiments. In each case 800 grams of a crude butyraldehyde obtained by oxo synthesis were vigorously stirred with 300 grams of a buffer solution while 10 liters/ hour of air were passed through. Depending on the pH value, the following oxidation periods were necessary for converting the cobalt carbonyl compounds into cobaltic salts:

time of oxidaature, C

With a pH value of 1.97, the formation of cobaltic salts in a comparable time could only be obtained when the temperature was raised. In this case, however, a marked aldehyde oxidation already takes place owing to the simultaneously increased reaction time. The oxidation of the iron carbonyl is accelerated by temperature increase; in general, however, a temperature of 10 to 30 C. is substantially suflicient. It is, however, also possible to proceed at a higher or lower temperature, for example at to 100 C.

By the process of the invention there are obtained, with splitting off of carbon monoxide, solutions of salts of the metals of the iron group from which solutions the metals can be recovered in various ways. It is a special advantage of the process of the invention that the metal compounds are obtained in a dissolved form without the addition of an acid so that they need not be filtered or washed until neutral. The present process offers the further advantage that the aldehydes obtained by distillation from the oxidation mixture containing the metal salts which are no longer volatile, are completely free from metal and as clear as water. If a mineral acid is added to the material to be distilled, completely colorless residues are left behind by the distillation which residues, after being washed until neutral, can be used directly as high boiling solvents, addition substances for plasticizers or as constituents for industrial emulsions and preparations.

The process of the invention may be conducted in various ways. It may be carried out continuously or discontinuously in a vessel provided with a stirrer by intimately mixing the crude aldehyde with water or an aqueous solution in the presence or with the introduction of a calculated amount of air until formation of the cobaltic salts is complete, which can be recognized by the green color of these salts. The aldehyde which is then free from iron carbonyl is directly distilled off or freed, after separation, from still adhering portions of dissolved metal compounds by washing with warm water or by adding small quantities of mineral acids.

The oxidation of the iron carbonyl can be effected in a particularly simple and advantageous manner when proceeding continuously. into a reaction zone, advantageously a tube provided with distributing devices, air and crude aldehyde may be introduced from one side, for example from below if a packed column in upright position is used, while at the same or a different place, for example at the head of the aforesaid packed column, the aqueous phase, i.e. an aqueous solution or water, is introduced. A zone of cobaltic salt formation rapidly forms which can be easily recognized by its green color and can be maintained at the desired level by appropriate adjustment of the supply of the reactants. ,It is also' possible to introduce the two liquid components together in countercurrent to the air or to conduct all reactants in the same direction.

Instead of fillers other distributing devices may be used. The use of a swing column, for example, is par ticularly simple as regards the construction of the apparatus if the swing plates are arranged stationarily and the liquid phase is intermittently moved.

The content of iron carbonyl in the crude aldehyde in general oscillates about an average value. A reliable oxidation is suitably achieved by introducing such an amount of air as is just sufficient to oxidize a small portion of the aldehyde, for example about 0.2 to 0.5%. The minimum time of stay can easily be determined by distilling a sample of the reaction product leaving the oxidation zone; as soon as iron carbonyl is found in the distillate, the time of stay is too short and must be prolonged.

With respect to the course of the reaction, it is assumed that in the absence of cobaltic salts the oxidation of iron carbonyl takes longer than the oxidation of the aldehyde so that complete destruction of the iron carbonyl is only possible with losses in aldehyde occurring. If, however, cobaltic salts are present, the latter either oxidize the iron carbonyl direct or convey the oxidizing action of the air preferably to the iron carbonyl compounds. These compounds which are dissolved in the crude aldehyde are therefore rapidly converted into nonvolatile soluble iron salts without appreciable losses in aldehyde.

The process of the invention can be used for removing iron carbonyl from products obtained by reacting olefins with carbon monoxide and hydrogen in the presence of cobalt catalysts such as Co (CO) or l-lCo(C0) The reaction mixture may furthermore be mixed with iron carbonyl as such. lron carbonyl compounds may also be formed by the reaction of carbon monoxide with iron compounds which have been added or with iron-containing material used for the container. The present process is, for example, applicable to the purification of reaction products obtained by the reaction of carbon monoxide and hydrogen with olefins containing 2 to 16 carbon atoms. Suitable olefins are, for example, ethylene, propylene, butylene, isobutylene, butadiene, pentene, heptene, ethylhexene, octene, tripropylene, diisobutylene, dodecylene, triisobutylene, hexadecene, cyclohexene, pinene, camphene and dipentene.

In the following the results obtained by the known processes are compared with those obtained by the process of the invention. The examples of the process of the invention serve to illustrate the invention but they are not intended to limit it thereto.

Known processes:

(A) The following tests prove the stability of iron carbonyl to a heat treatment with mineral acids:

(at) 800 grams of a crude product obtained by an addition reaction of carbon monoxide and hydrogen with ethylene and containing 75.6% of propionaldehyde and 0.12% of cobalt (dissolved in the form of cobalt carbonyl compounds) were heated with 200 grams of 0.1 N-sulfuric acid under nitrogen. The aldehyde fraction passing over at 48 C. had a deep yellow coloration. It

, was free of cobalt but contained iron in a concentration of 0.008%. After standing for 1 day, a great part of the iron had deposited at the bottom of the vessel in the form of hydroxide; the supernatant aldehyde was still slightly yellow. 7

(B) By way of comparison, -a similar test was carried out using a crude product which had been obtained' by addition reaction of carbon monoxide and hydrogen with propylene. 500 grams of this product containing 0.31% of cobalt (dissolved in the form of cobalt carbonyl compounds) and 0.12% of iron (dissolved in the form of iron carbonyl) were heated with 100 grams of 0.1 N-sulfuric acid. At a filling column of a filling height of 80 centimeters adistillate of 374 grams was obtained which passed over at a temperature up to 95 C. By means of a fractionating column the condensate was separated into an aqueous and an organic phase and the aqueous phase was returned to the column after the organic phase had been removed. The first portions were deeply ocher-colored while the last portions showed a light yellow coloration. The filling bodies of the undermost zone were coated with metallic cobalt and on the wall of the flask a layer (mirror) of metallic cobalthad formed. In the distillate no cobalt could be detected but 0.02 gram of iron dissolved in the form of carbonyl and a further 0.01 gram of iron in the form of hydroxide.

(B) The stability of the iron carbonyl to oxidation is shown by the'following tests:

(a) 400 grams'of a crude aldehyde obtained by addition reaction of carbon monoxide and hydrogen with diisobutylene and containing cobalt and iron were intimately mixed with 100 grams of Oil N-sulfuric acid in a flask provided with a stirrer. At the same time 10 liters/hour of air were introduced. After 20 minutes the current of air was withdrawn and the crude product the color of which had turned from brown to a light pink was distilled off with the use of the fractionating column described in test A, p. The first 200 grams passed over in the form of a yellow liquid from which iron hydroxide gradually separated on standing. The same result was obtained in a test in which the oxidation was carried out in the presence of acetic acid instead of sulfuric acid.

(18) A similar test was carried out with a crude butyraldehyde containing 0.085% of cobalt and 0.0086% of iron dissolved in the form of carbonyl compounds. 1000 grams of this product were vigorously stirred for 35 minutes at 23 C. with 300 grams of 0.1 N-sulfuric acid, while 10 liters/hour of air were passed through. During this time cobaltic salts which are recognizable by their green coloration were not formed. The originally brown color became lighter and turned pink. The product separated immediately and smoothly into a colorless aldehyde layer and a clear pink acid layer. The latter contained 745 mil ligrams of cobalt and 8 milligrams of iron, i.e. 88% of the cobalt and 9.3% of the iron had passed over into the aqueous phase in the form of cations. The aldehyde was then distilled with steam with addition of 300 grams of 0.1 N-sulfuric acid, during which procedure 972.5 grams of a turbid yellow distillate passed over at a temperature up to 96.5 C. 262 grams of the acid Were eft behind in the flask; they contained 68 milligrams Co and 25 milligrams Fe, i.e. a further 8% and 29% of the respective metals dissolved in the form of cations. Bv combining an oxidation carried out in the absence of cobaltic salts with a steam distillation conducted in the presence of a mineral acid there were thus recovered 96% of the cobalt but only about 40% of the iron. The distillate was free of cobalt but contained 44 milligrams of iron. i.e. 52% of the iron originally present, which iron was found in the distillate in the form of undestroyed iron carbonyl.

(C) The following test shows the results obtained in the absence of compounds of trivalent cobalt:

2 kilograms of crude aldehyde, obtained by addition reaction of water gas with ethylene, and 8 liters of air were introduced from below, per hour, into a vertically arranged glass tube filled with Raschig rings and having a height of 2 meters and a free volume of 1 liter. At the same time 500 grams/hour of 0.1 N-sulfuric acid were introduced from above. The aqueous layer was discharged at the lower end of the tube. The aldehyde was removed together with the air at the upper end of the tube and separated from the air in a separator. From the separator the aldehyde was fed to the middle section of a distilling column having a height of 2 meters into the distilling vessel of which 2 liters of 0.1 N-sulfuric acid had been introduced. The propionaldehyde drawn off at the head of the column had a deep yellow coloration and contained 0.0025 of iron dissolved in the form of carbonyl as under the conditions indicated no cobaltic salts had formed in the oxidation zone.

Examples of the process of the invention:

Example 1 As soon as in test C described above the supply of sulfuric acid was reduced by 50%, while otherwise proceeding under the same conditions, formation of cobaltic salts set in due to the altered concentration of hydrogen ions. The brown liquid in the tube assumed the green coloration characteristic of these salts and the propionaldehyde drawn off at the head of the column was completely colorless and free of metals. The same result was obtained by increasing the quantity of air used. When, however, the supply of air was reduced or the supply of acid was increased to such an extent that the formation of cobaltic salts was suppressed since at the low pH value the residence time was too short for an oxidation, iron-containing yellow aldehyde was obtained at the head of the column. This change could be repeated as often as desired and clearly demonstrates the influence of the concentration of hydrogen ions upon the formation of the cobaltic salts and their importance for the oxidative destruction of iron carbonyl.

Example 2 1000 grams of the crude butyraldehyde mentioned above in test B, B were vigorously stirred for 35 minutes at 23 C. with 300 grams of a 5% NaHCO solution, while 10 liters/hour of air were passed through. After 5 minutes the formation of cobaltic salts could be recognized by a green coloration which rapidly grew deeper. After 25 minutes this coloration remained constant. In the dark green water layer 760 milligrams of cobalt and 48 milligrams of iron could be detected. Thus, 89% of the cobalt and 56% of the iron had passed over into the aqueous phase in the form of cations. 911 grams of the aldehyde were then fractionated with addition of 302 grams of 0.1 N-sulfuric acid in the fractionating column described above in test A, 5. At a temperature up to 96 C., 863

grams of a completely clear colorless distillate passed over. The acid layer remaining behind in the flask contained 90 milligrams of Co and 38 milligrams of Fe, i.e.

' 11% and 44% of the respective metals. When working under the conditions described above sub B but proceeding in the presence of cobaltic salts both the cobalt .and the iron were thus completely recovered in the form of cations. The distillate was completely free from cobalt and iron.

Example 3 In a test carried out according to Example 1 while using a tube of a free volume of 2 liters, 2 kilograms/ hour of a crude butyraldehyde obtained by addition reaction of water gas with propylene were treated with 20 liters/hour of air. Instead of 0.1 N-sulfuric acid, distilled water was introduced from above into the tube. The aqueous layer was discharged at the lower end of the tube. The aldehyde was drawn off together with the air at the upper end of the tube and introduced into a separator from where it was fed in one case to the middle part of a distilling column and in another case introduced into a washing tower containing water at 60 C., in order to be freed from any still adhering portions of metal salts. Immediately above the entrance for the aldehyde, formation of a green zone set in and the upper half of the tube showed the uniform green color of the cobaltic salts formed. At the lower end of the tube a dividing line between aldehyde and water was kept at a constant level by appropriate adjustment of the water discharge. It was ascertained by preliminary tests that in the case of the crude aldehyde used a medium suitable for the rapid formation of cobaltic salts was obtained by adding 20 to 30% of water in counter-current and that a time of stay of 15 minutes at 20 C. was sufficient for the destruction of the iron carbonyl.

On consecutive days the following characteristic values of the crude aldehyde (a) and the aldehyde which had been treated with air (b) were ascertained:

Percent Percent aldehyde acid (in the l.lh. l./h. l./ h. (in the iorm form of an" d4" alde- H1O air of butyralbutyric hyde dehyde) acid) 53. 7 l. 4 1.4014 0.858 6 1. 6 50 53. l 2. 2 1.4024 0. 861 59. 0.5 1.4010 0. 840 6 l. 6 50 58. 6 1. 4 1. 4014 0. 845 67. 5 0. 4 l. 3964 0. 835 6 1. 5 15 67. l 0. 8 1. 3969 0. 840 66.9 0. 1 l. 3989 0. 832 6 1. 5 15 66.5 0.5 l. 3989 0. 839

The aldehyde which had been treated with air was completely free of volatile metal carbonyl compounds and yielded a water-clear product after distillation.

Example 4 A circulating apparatus consisting of two vertically arranged empty glass tubes connected with each other at their upper and lower ends and having a length of 3 meters, one tube having an inside diameter of 7 centimeters and the other tube having an inside diameter of 3 centimeters, was filled with crude propionaldehyde containing 0.1% of cobalt and 0.04% of iron dissolved in the form of carbonyl compounds and furthermore containing 1.1% of water originating from the manufacture of the propionaldehyde. At the lower end of the tube having an inside diameter of 7 centimeters, 30 liters/hour of air were blown in through a frit, whereupon the circuit of the product set in. After the light yellow product had assumed a deep black-green coloration at a pH of 6.2 due to the formation of cobaltic salts, l2 liters/hour of crude product were continuously introduced into the lower part of this tube. A corresponding quantity of a product free from carbonyl was drawn off by means of overflow at the upper end of the tube having an inside diameter of 3 centimeters and introduced into a distilling column, the distilling vessel of which was charged with 2 N-sulfuric acid. At the head of the column water-clear propionaldehyde free from any traces of metal was drawn off. When the air was replaced by nitrogen, the crude product retained its light yellow color and the propionaldehyde distilled over with a yellow to brown coloration and contained iron.

We claim:

1. A process for removing iron carbonyl from a crude oxo reaction product, which process comprises contacting said crude oxo reaction product, at a' pH in the range from about 3 to 9, and at a temperature in the range from about 0 to C., and in the presence of water and trivalent cobalt produced by oxidation of cobalt carbonyl dissolved in said crude oxo reaction product, with an amount of oxygen sufiicient to oxidize said iron and cobalt carbonyls to water soluble salts of these metals, and recovering said oxo reaction product free of said metal salts.

2. A process for removing iron carbonyl from a crude oxo reaction product, which process comprises contacting said crude oxo reaction product, at a pH in the range from about 3 to 9, and at a temperature in the range from about 0 to 100 C., and in the presence of water and trivalent cobalt produced by oxidation of cobalt carbonyl in said crude oxo reaction product, with a gas containing molecular oxygen, said oxygen being in an amount sufiicient to oxidize said iron and cobalt carbonyls to water soluble salts of these metals, and recovering said oxo reaction product free of said metal salts.

3. A process for purifying a crude oxo reaction product containing from about 0.1 to 5 percent by weight of water and having a pH in the range from about 3 to 9, which process comprises passing a gas containing molecular oxygen through said product at a temperature in the range from about 0 to 100 C. to oxidize iron carbonyl and cobalt carbonyl in said oxo reaction product until a green color of trivalent oxidized cobalt is produced in said oxo reaction product, and then distilling the product thus obtained to obtain said oxo reaction product tree of dissolved metal compounds.

4. A process as claimed in claim 1 wherein the oxidation of the iron carbonyl is carried out at a pH in the range from about 4 to 6.

5. A process as defined in claim 2 wherein the oxidation of the iron carbonyl is carried out at a temperature in the range from about 10 to 30 C.

6. A process as claimed in claim 1 wherein the oxidation of the iron carbonyl is carried out in the presence of an amount of water in the range from about 0.1 to 5% of weight calculated upon the total weight of the oxo reaction product.

7. A process as claimed in claim 3 wherein the molecular oxygen is used in at least the stoichiometric amount calculated upon the amounts of the metal carbonyl compounds in the crude oxo reaction product.

References Cited in the file of this patent UNITED STATES PATENTS 2,604,491 Hale July 22, 1952 2,758,l36 Buchner Aug. 7, 1956 2,763,694 Buchner et al. Sept. 18, 1956 2,810,680 Buchner et al. Oct. 22, 1957 FOREIGN PATENTS 726,135 Great Britain Mar. 16, 1955 

1. A PROCESS FOR REMOVING IRON CARBONYL FROM A CRUDE OXO REACTION PRODUCT, WHICH PROCESS COMPRISES CONTACTING SAID CRUDE OXO REACTION PRODUCT, AT A PH IN THE RANGE FROM ABOUT 3 TO 9, AND AT A TEMPERATURE IN THE RANGE FROM ABOUT 0* TO 100*C., AND IN THE PRESENCE OF WATER AND TRIVALENT COBALT PRODUCED BY OXIDATION OF COBALT CARBONLY DISSOLVED IN SAID CRUDE OXO REACTION PRODUCT, WITH AN AMOUNT OF OXYGEN SUFFICIENT TO OXIDIZE SAID IRON AND COBALT CARBONLYS TO WATER SOLUBLE SALTS OF THESE METALS, AND RECOVERING SAID OXO REACTION PRODUCT FREE OF SAID METAL SALTS. 